In that time, he has built an unconventional practice representing best-selling authors, political leaders, television news correspondents and other high-profile clients.

In addition to Mr Obama and Mrs Palin, other authors he has represented include novelist Mary Higgins Clark and entertainer Barbra Streisand.

He has also helped former government officials from across the political spectrum navigate their return to private life, including former US presidents Bill Clinton and George W Bush, former secretary of state Madeleine Albright, and former members of Congress.